{
  {
      "_id": "someid|goes|here",
      "collected": {
          "tags": ["abc", "def", "ghi"]
      }
  },
  {
      "_id": "someid1|goes|here",
      "collected": {
           "tags": ["abc", "klm","pqr"]
      },
  },
  {
      "_id": "someid2|goes|here",
      "collected": {
           "tags": ["efg", "hij","klm"]
      },
  }
}

{
   "selector": {
      "collected.tags": {
         "$regex": "abc"
      }
   }
}